On May 20, 2015, David Letterman will sign off of "The Late Show with David Letterman" for the last time. We look back here on memorable moments in his television career. Jeffrey R. Staab, CBS

Stephen Colbert, future host of the "Late Show," talks to David Letterman on April 22, 2014. Jeffrey R. Staab, CBS

Bill Murray spray paints Dave's desk on the first taping of the "Late Show with David Letterman" on Aug. 30, 1993, on CBS. Alan Singer, CBS

Bill Murray joined Dave for the 20th anniversary of the "Late Show" on Aug. 29, 2013. Murray retrieved a time capsule as part of the festivities. John Paul Filo, CBS

Oprah Winfrey returns to chat with David Letterman on Dec. 1, 2005, 16 years after her previous visit. Jeffrey R. Staab, CBS

Drew Barrymore turns to the audience after flashing David Letterman on his birthday on April 12, 1995. Alan Singer, CBS

David Letterman holds a photo of his new son, Harry Joseph Letterman, on Nov. 4, 2003, the day after he was born. John Paul Filo, CBS

Steve Martin, left, feigns sleep after asking David Letterman to tell him about his new baby. John Paul Filo, CBS

Tom Hanks surprises Julia Roberts and David Letterman when he drops by the the "Late Show." Letterman tested Roberts' knowledge of Hanks "Newlywed Game"-style, asking her questions about the actor. Heather Wines, CBS

Demi Moore brought an action-figure physique while promoting her film "G.I. Jane" on July 2, 1996. Alan Singer, CBS

Paul Shaffer helps David Letterman dole out pies in the face to Regis Philbin as Letterman and Philbin toss pies at each other in tribute to the passing of comedian Soupy Sales in October 2008. John Paul Filo, CBS

Dea Devlin, 12, from Brooklyn, N.Y., jumps on a pogo stick and plays a violin while Letterman looks on during Stupid Human Tricks in November 2009. Jeffrey Neira, CBS

Stupid pet tricks like this one from November 2012 were a staple routine. Heather Wines, CBS

Johnny Carson in his first and only talk show appearance since stepping down as host of "The Tonight Show," gets a standing ovation by Letterman and the studio audience when he makes a surprise appearance on the "Late Show" on May, 13 1994. Tony Esparza, CBS

Letterman hosted President Obama in September 2012. Carolyn Kaster, AP

Letterman interviewed Paul McCartney and Ringo Starr for a CBS special 'The Beatles: The Night That Changed America - A Grammy Salute' in February 2014. Letterman's show is taped in the Ed Sullivan Theater in New York, the same theater where the Beatles made their American debut in 1964. Jeffrey R. Staab, CBS via AP

Cher chats with Letterman during a taping in September 2013. Jeffrey R. Staab, CBS via AP

An ailing Jennifer Lawrence snuggles in a blanket as Letterman laughs from the desk on the set in November 2013. Jeffrey R. Staab, CBS via AP

Letterman was a recipient of the 2012 Kennedy Center Honors, along with Dustin Hoffman and and bluesman Buddy Guy in December 2012. Manuel Balce Ceneta, AP

Letterman appears as a guest with Johnny Carson, the host of the 'Tonight Show.' Carson died in 2005. AP

In a rare television appearance, Paul Newman visits with Letterman in 1994. Alan Singer, CBS

Letterman reacts as Madonna arrives on stage bearing Valentine's Day gifts in February 1995. Madonna dropped by Letterman's show to wish him a happy Valentine's Day and promised, "I'm not going to say (bleep) any more." It was the singer's first return to the show since her notorious March 31, 1994, appearance when she had to be bleeped by CBS censors a total of 13 times. Alan Singer, CBS

Letterman looks on as musical leader Paul Shaffer, center, bites into a fried baloney sandwich made by Dave's mom, Dorothy, left, in 1996. Dorothy was promoting her new cookbook, 'Home Cookin' with Dave's Mom.' Letterman said as a kid he'd have a fried baloney sandwich "every day, two or three times a day, especially when mom slept late." CBS via AP

Farrah Fawcett behavior during an appearance on the show in 1997 raised a few eyebrows. CBS

Letterman gestures during his interview with Hillary Rodham Clinton in January 2000. She made her first visit to the show, a stop that follows weeks of the late-night host taking pot-shots at Clinton over her decision to relocate and her intention to run for U.S. Senate in New York. Barbara Nitke, CBS

Joaquin Phoenix stayed in character, as himself in the mock-documentary 'I'm Still Here,' in February 2008. John Paul Filo, CBS via AP

Jennifer Garner watches as Letterman applies ointment to her scraped knee in April 2009. Garner had fallen while running. John Paul Filo, CBS via AP

Robin Williams laughs while exchanging heart surgery stories with Letterman in May 2009. It was Williams' first television appearance since his heart surgery eight weeks earlier. John Paul Filo, CBS via AP

One of the nightly features on the 'Late Show' was the 'Top Ten' list. Britney Spears presented the 'Top Ten Ways the Country Would Be Different if Britney Spears Were President' in August 2009. CBS via AP

In a highly personal and public moment in October 2009, Letterman talks about having had sexual relationships with female employees and how a CBS employee tried to extort $2 million from him over the affairs. CBS via AP

Denzel Washington jokingly shows Letterman some of his martial arts moves in January 2010. John Paul Filo, CBS via AP

Kiefer Sutherland makes good on a weekend football bet by wearing a dress to the set in January 2010. Worldwide Pants Inc. via AP

Letterman rides a go-cart powered by the reaction from mixing 648 Mentos candies into 108 two-liter bottles of Coke in June 2010. Charles Sykes, AP

Former President Bill Clinton visited the show in September 2010. Jeffrey R. Staab, AP

Paris Hilton shows Letterman some features of the Paris Hilton smartphone app in February 2011. John Paul Filo, CBS via AP

Letterman and Matt Damon pose for a holiday greeting card in December 2011. John P. Filo, CBS via AP

Bill Murray attempts a field goal on New York's 53rd Street with Letterman doing the holding in January 2012. John Paul Filo, CBS via AP